sedimentary
Chert (Jasper/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: tan, brown, or pinkish-beige, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none, Fracture: conchoidal (shell-like curves), Specific gravity: 2.6
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: tan, brown, or pinkish-beige, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none, Fracture: conchoidal (shell-like curves), Specific gravity: 2.6
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical replacement of existing rocks by silica-rich fluids in aquatic environments.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges when fractured. Currently used in aquarium gravel, garden decor, and occasionally as a semi-precious gemstone when polished.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its historical use as 'flint' in flintlock firearms. It is incredibly resistant to chemical weathering.
Field identification & locations
Identify in the field by its waxy texture and conchoidal fracture (curved breakages similar to thick glass). It cannot be scratched by a steel knife. Common in limestone regions or as rounded river cobbles.
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